My advice from personal experience is not to use synthetics in the transmission. I had a Porsche 928 (which uses a Mercedes automatic) that did not leak until an overachieving mechanic recommended Mobil One. Thereafter it leaked out the rear seal and changing back to regular did not help. The mess on the garage floor was bad enough, but it got onto the exhaust pipes which caused a nauseating stench.

My advice is that if the car does not leak, do not do anything that might cause it to start.

Frank King, the late Tech Director for the Mercedes Club was adamant about not using synthetics.